Essential Health & Safety Requirements | 43
Field Unit Electronics
Power Distribution
• The AC supply is applied through circuit breaker CB1 and thermal
cutout S2 to the primary of transformer T1.
• The T1 secondary (35 VAC) is connected directly to rectifier and regu-
lator circuits on the electronic control board.
• Diodes CR4 and CR5 supply unregulated +24 volts and feed the
series-connected voltage regulators.
• VR1 supplies +12 volts and VR2 supplies +5 volts.
• Diodes CR2 and CR3 supply unregulated +24 volts for the cell oven.
• CR15 and CR16 supply unregulated +24 volts for the moisture gen-
erator oven.
Power distribution failure symptoms
• Valves do not switch, but output reading could be on display.
• One or more LEDs do not light, depending on faulty circuit.
• No moisture generator heat.
• No oven heat; CR1 and CR14 on steady.
Electronics control board voltage checks
• +5 volts — TP5 J7
• +12 volts — TP4 J6
• +24 volts — TP2 J4 (0 volt — TP1 J3)
Heat Control
There are two, identical, +24-volt heat control circuits: one for the cell oven and one for
the moisture generator. Each has a heater, an inverting amplifier (U1 or U2), a thermistor
(RT1 or RT2), a triac (Q1 or Q2), an LED (CR1 or CR14), a temperature adjustment pot
(R17 or R26), and miscellaneous resistors and capacitors.
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